REPORT ON THE MOLLUSC A. 15 



possess two laminse, but they correspond to the two himinse of 07ie branchial plate in 

 the Pelecjrpoda, — a direct and a recurrent or reflected lamina. Tlius the gill of Lucina 

 and that of Cryptodon moseleyi correspond to only one of the branchial plates of 

 other Pelecypoda, — the inner one, as we shall see later (PI. lY. fig. 4). 



As to the "pallial gills" mentioned by Semper, we have seen above that these are 

 probably only the thickened edges of the mantle. 



15. Cryptodon luzonicus, ^mith. Station 205 ; 1050 fathoms. 



The structure of this species is exactly similar to that of the preceding, especially 

 as regards the foot, the gill, and the mantle, this last having also only one posterior 

 anal aperture (PI. II. fig. 5). 



Smith ^ has expressed his douljts as to the synonymy of the two names Axinus 

 and Cryptodon, — a synonymy admitted, one may saj^, by all authors. 



Axinus was used in 1821 by J. Sowerby for a fossil, Lucina angulata, whose 

 structure is, of course, unknown. 



Cryptodon was created in 1822 by Turton for a living Pelecypod, Lucina 

 Jlexuosa, Montagu, which all writers have since placed in the above-named genus 

 Axinus, imjjlying the synonymy of the generic names given by Sowerby and Turton. 



I have unfortunately been unable to procure a specimen of the animal of 

 "Axinus" Jlexuosus, so that I could not studj^ it for myself But Jeffreys^ has 

 already pointed out that this form possesses " two gills on each side ; " and the 

 structure of the genus Axinus or Cryptodon is particularly well known through the 

 work of Sars,' who has studied in detail Axinus sarsi, Philippi, a species allied to 

 Axinus Jlexuosus. 



Sars confirms Jeff'reys' statement, that there exist two gills on each side, similar to 

 those of the typical Pelecypoda.^ 



In Axinus sarsi, the visceral glands (hepatic and genital) form a projection outside 

 the pedal muscular wall, and their ramifications extend freely into the visceral cavity 

 on each side of the foot (an arrangement which I have hitherto observed only in 

 Montacuta ferruginosa, which I was able to study in great abundance in Prof Giard's 

 laboratory at Wimereux). The foot is filiform, very long, and directed backwards. 

 There is only one pallial aperture, with no siphon, and the gills do not become united 

 to the pallial commissure separating the anal from the great branchio-pedal aperture. 



These animals {Axinus Jlexuosus and Axinus sarsi) diff'er entirely from our 

 " Cryptodon " in regard to the gills, the foot, and the arrangement of the visceral 



' Zool. Chall. Exp., part xxxv. p. 187. ^ British Coiicliology, vol. ii. p. 245. 



3 .Malaoozoologiske Jagttagelser, i. Om Dyret af Cryptodon Sarai (Axinus), Philippi, Forhandl. VidensL 

 Selsl: ChrMania, 1864, pi. iv. fig. 11. 

 * Sars, he. cil., pi. iv. fig. 4, li. 



